Heat resistant alloys of iron, cobalt and/or nickel and articles thereof

ABSTRACT

Alloys of iron, cobalt and/or nickel containing from 0.5 to 4.0% carbon and from 5 to 60% tungsten, molybdenum or mixtures thereof characterized by the absence of &#39;&#39;&#39;&#39;reactive&#39;&#39;&#39;&#39; elements such as Cr, V, Cb, Ta, Ti, Si, Mn and Al. which form hard-to-reduce oxides.

United States Patent Holtz, Jr. et al. [451 Oct. 17, 1972 HEAT RESISTANTALLOYS OF IRON, [56] References Cited COBALT AND/OR NICKEL AND ARTICLESTHEREOF UNITED STATES PATENTS 721 inventors: Frederick c. Holtz, Jr.,Evanston, 299L017 8/1937 f X g Ivlol.row Ann Arbor Hams R 5, 3,244,5064/1966 Reen ..75/o.s

[ Assigneei Crucible, Illc- Primary Examiner-Dewayne Rutledge AssistantExaminer--.l. E. Legru 22 F] d. D 2 1 l 6 BC 8 1970 AttrneyClalr X.Mullen, Jr. 211 Appl. No.: 102,203

Related US. Application Data [57] ABSTRACT Continuation-impart 0f N0 yAlloys of iron, cobalt and/or nickel containing from 1963, abandoned-0.5 to 4.0% carbon and from to tungsten, molybdenum or mixtures thereofcharacterized by the 29/l82.5, absence ofreactive elements such as Cr,V, Cb, Ta,

75/12 75/123 75/123 34 Ti, Si, Mn and Al. which form hard-to-reduceoxides.

75/170, 75/176 [5 l] Int. Cl. ....C22c 39/10, C22C 39/36, C220 39/50[58] Field of Search ..29/] 82.7, 75/l23, 0.5 BC, 7 Claims, No DrawingsHEAT RESISTANT ALLOYS OF IRON, COBALT AND/OR NICKEL AND ARTICLES THEREOFThis application is a continuation-in-part of application Serial No.743,92l,f1led July 11, 1968 by the same inventors and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to heat-resistant alloy articles and particularly to aninexpensive heat-resistant alloy which is readily workable and castable.The present invention provides alloys which are not only heat-resistantbut have excellent strength and hardening ability and have particularutility in the fabrication of cutting tools, dies and wear parts, or foruse as a structural alloy.

2. Description of the Prior Art The development of alloys based on iron,cobalt, and nickel has been characterized by increasing emphasis on theability of these materials to withstand elevated temperatureenvironments. The structural alloys are used for such applications asturbine buckets, nozzle vanes, rotor discs, combustion liners, and otherturbojet engine parts, as well as furnace parts, exhaust manifolds, highpressure steam piping, valves, and other fittings which must sustainloads at high temperatures. In addition, there are numerous tool and dieapplications which require both strength and wear resistance at elevatedtemperatures. These include tools for metal cutting and the manymetalworking operations such as swaging, forging, rolling, wire drawing,shearing, and extrusion'which are carried out under severe conditions ofheat and sliding friction.

These thermal-resistant tool, die, and structural materials may be madeby various techniques such as casting directly to shape, forging orrolling, and powder metallurgy. Their major constituent may be iron,nickel, or cobalt, and they are further strengthened by a wide range ofalloying elements. However, they have one characteristic in common: allcontain additions of reactive metals. A reactive metal is an elementcharacterized by a high negative value for the free energy of formationof its oxide or oxides. Stated in another way, the oxides of reactivemetals are increasingly difficult to reduce to the metallic state as thefree energy of formation rises to higher negative values. For thepurpose of this discussion, a value of -40K cal/gram-atom of oxygen at1,500 K. represents the dividing line between reactive and non-reactive.Thus M 0 with a value of -32K cal/gram-atom can be reduced by the H orother reductants at comparatively low temperatures, i.e., l,600 F.,while A1 0 with a free energy -=95K cal/gram-atom is reducible only atextremely high temperatures.

An examination of compilations of thermal-resistant tool, die andstructural alloys of the prior art shows that all conventionalcompositions contain chromium (-58K cal/gram-atom). A listing of 30commercial nickel-base high-temperature alloys gives a range of to 27percent chromium. A similar listing giving compositions of thethermal-resistant cobalt-base tool alloys which have been marketed showsa chromium range of 18.5 to 31 percent. All 29 commercial high speedsteels (AlSl designation T and M series) contain 3.75 to 4.25 percentchromium, and the 18 A181 type H hot die steels contain from 2 to 12percent of this reactive element.

Chromium is added to these alloys primarily because of its beneficialeffect upon oxidation resistance and, in the case of tool steels, itsability to give a moderate increase in the depth of hardening. ltsprimary drawback is the fact that its oxides are extremely difficult toremove by chemical means. Other reactive elements are also-added tonearly all of the iron, cobalt and nickel thermal-resistant alloys.These elements include AL, Cb, Mn, Si, Ta, Ti, V, Zr, etc. Theseelements generally promote alloy strengthening or wear resistance but,as in the case of chromium, their oxides are also very difficult toreduce. Alloys containing reactive metals suffer an additionallimitation in that during melting, the reactive elements present requireadditional protection from the atmosphere and they also react withcommon refractory crucible materials such as alumina, magnesia, silica,etc. This means that inert atmospheres such as argon or a vacuum andextremely inert crucible materials (beryllia, thoria, zirconia) be usedor else melting must be done by arc-melting in a water-cooled coppercrucible. There are obvious economic drawbacks in using these specialmelting methods.

SUMMARY OF THE INVENTION The present invention provides athermal-resistant alloy free of reactive elements such as chromium andvanadium, consisting essentially of about 0.5 percent to 4.0 percentcarbon, about 5 percent to 60 percent of a carbide-former selected fromthe group consisting of nonreactive elements, such as tungsten,molybdenum and mixtures thereof, and the balance being M with usualimpurities in ordinary amounts, wherein M is base metal selected fromthe group consisting of iron, cobalt, nickel and mixtures of two or moreof these elements. Such alloys exhibit increased cutting speedcapabilities and wear resistance by providing structures free fromembrittling oxides, thereby permitting higher carbide volumes and largercontents of refractory metal alloying elements such as tungsten andmolybdenum which appreciably improve the elevated-temperature strengthproperties. These alloys are harder than any heretofore known cast orwrought tool or die alloys based on iron, nickel or cobalt, and theygave cutting performance far superior to the conventional tool steelswhich were tested for comparison purposes. Further, such alloys havebeen found to have excellent high temperature strength, very hightransverse-rupture bending strength, exceptional response to heattreatments, very high fabricability, and the ability to be produced fromvery low cost powders.

Also provided by the present invention are structural alloys for use inapplications where great strength at high temperature is required. Suchalloys are prepared by reducing the carbon content of the alloycomposition set forth above to lower the hardness of the alloy to Rc orbelow and increase the toughness. The solidsolution strengtheningprovided by the high tungsten and molybdenum levels results in alloyswhich are capable of withstanding severe mechanical stress at elevatedtemperatures above about 700 F. for prolonged periods of time. Moreover,these new tool and structural alloys, can be produced with an ultrafineOxides Formed by Free Energy Reactive" Elements of Formation (l500K) V0, 48 0,0, 58 mp, 62 MnO --66 T3203 *67 z -72 Tao -80 mp, 95

Oxides Formed by Free Ener Nonreactive" Elements Of Formal-I011 NiO 27C00 27 MoO -32 W0: 38 F9304 -38 DESCRIPTION OF THE PREFERRED EMBODIMENTSThe broad composition of alloys within the present invention is asfollows:

About 0.5 4.0 percent carbon About 5 60 percent of a non-reactiveelement whose oxides are easily reduced at low temperatures, and theremainder being M with usual impu rities in ordinary amounts, wherein Mis iron, cobalt, nickel or a mixture of two or more of these elements.All of the alloys are characterized by the complete absence of reactiveelements such as Cr, V, Cb, Ta, Ti, Si, Mn and Al.

Molybdenum and tungsten are non-reactive elements which are carbideformers. Each may be absent altogether or present up to a maximum of 60percent. Accordingly, the outside limits of such use in accordance withthe present invention are:

Mo about 0 60% W about 0 60% Mo W about 5 60% The invention will bebetter understood by a consideration of the examples wherein the variousembodiments will be brought out in detail. Several differentcompositions of material were melted to form an alloy according to thisinvention. Illustrative compositions of these materials are given inTable I.

TABLE I Alloy Compositions, Weight Percent alloy Fe Co Ni W Mo A76 4547.25 5 2.75 A81 62.5 10 25 2.5 A82 37.510 45 s 2.5 A83 42.5 20 10 252.5 A91 37.5 10 35 is 2.5 106 57.5 40 2.5 A113 56.5 40 3.5 A136. 58.7 2020 1.3 M37 38740 20 1.3 A138 53.7 20 25 1.3

A146 28.1 50 20 1.3 A147 38.7 40 1o 10 1.3 A151 38.7 40 20 1.3 A152 38.939.9 19.9 1.3 A163 39.2 40 20 0.8 A164 38.33 40 20 1.67 A165 39.2 40 200.8 A169 34 34.7 30 1.3 A170 34 34.7 30 13 A171 34 34.710 20 1.3 A172 3434.710 20 1.3

articles made therefrom can be produced free of deleterious oxides bychemical deoxidation procedures.

It is a feature of this invention that metal and metal powders of thedefined composition characterized by the absence of the "reactiveelements chromium, vanadium, columbium, tantalum, titanium, silicon,manganese and aluminum, are easily reduced chemically and oxidesremoved, e.g., by using carbon present in the alloy composition as areducing agent. In this process, an alloy powder is jacketed in athin-walled container, and the canned powder heated to a temperature inthe range of about l,700 to 2,l00 F. A small vent can be provided forescaping gases of CO and C0,. However, it is not necessary that a ventbe provided or that the container be evacuated. 100 percent dense,oxide-free alloy stock is produced by extruding the self-cleaned powderinto a bar and removing the jacketing material. Alternatively, theheated canned powder can be consolidated by hot pressing followed byforging, rolling and removal of the cladding.

It has also been found that it is not necessary to jacket the powders inorder to remove oxide films from powders which have low softeningtemperatures. For example, in the case of the tool steel powders, cobaltand nickel structural alloy powders, and some cobalt base tool alloypowders, which can be softened by annealing in the temperature range ofabout l,400 to l,700 F the alloy powders can be cleaned and softened inone step by heating them to such temperature in a reducing atmosphere ofhydrogen, cracked ammonia, a hydrocarbon gas, such as methane, a mixtureof CO and CO or the like. After annealing the powder by slow cooling, itcan be cold pressed at room temperature to form an easily handledbillet. Subsequently, the billet of material is heated to about 2,000 F.in a protective atmosphere such as nitrogen, argon or the like, andextruded into 100 percent bar stock.

As a specific example of the process for making an oxide-free alloy inaccordance with the present invention, the production of alloy A 138 ofthe foregoing Table I will be considered in detail. In this example thealloy is made by powder metallurgy process, although it is to beunderstood that other methods of producing a1- loys can also be used.

An appropriate alloy charge, e.g., 5 pounds, of the desired composition(C0 20W 25Mo 1.3C) was weighed out, melted in an induction furnace (orother suitable melting device), and atomizedl. quenched using aconventional atomizer. Suitable apparatus is disclosed in copendingapplication Ser. No. 435,733, entitled Alloy Composition and Processfiled Feb. 26, 1965, by the present inventor. The molten stream wasbroken up into fine particles which were quickly quenched by the highpressure inert gas stream and by the water utilized asa collectionmedium. The oxygen content of dried alloy powderproduced in this mannerwas in the order of about 500 1,000 part per million.

The atomized alloy powder was then consolidated into solid stock by thefollowing process. The powder was first enclosed in a sealed Inconel canwithout evacuation and with no provision for venting gas formed duringsubsequent heating. The welded can was heated to a temperature ofapproximately 2,050 F.

prior to open-die, upset hammer forging on a 250 pound capacitymechanical forge unit. Forging was used to produce pancake ingotsapproximately one-half inch thick. After forging, the canned billetswere hot rolled to approximately 0.22 to 0.24 inches using a percentreduction per pass, this representing a total reduction in thickness of90 to 92 percent of the original billet thickness. The cladding materialwas then removed and the rolled plate stock sectioned for metallurgicalexamination and mechanical property evaluations. Visual examination ofphoto-micrographs of the consolidated powder showed that the alloy stockwas free of oxides and exhibited an ultrafine microstructure. Additionalproperties demonstrating that adequate hardness and thermal stabilityhad been achieved were apparent from the following measurements:

Hardness, as-rolled Re 60.6 Hardness, aged at 1300F. Re 66.6 coarseningtemperature 2350F.

By lowering the carbon content of alloy A 138 (e.g., to 0.5 percentcarbon) the hardness falls to a level below Rc 56 permitting use as astructural alloy. The alloy is readily hot-workable and has the abilityto withstand severe mechanical stress at elevated temperatures above 700F. for prolonged periods of time due to the so1id-solution strengtheningprovided by the high tungsten and molybdenum levels.

The alloys of the present invention were tested for hardness and bendtests were conducted at room temperature to ascertain transverse rupturestrengths. Data illustrating the test results are given for exemplaryalloys in Table 11.

TABLE 11 Alloy Properties The foregoing test results demonstrate thatthe tool alloys of the present invention possess excellent strength andare capable of exhibiting high hardness levels.

Cutting tests were performed using exemplary alloys of the presentinvention by operating the tools in comparison with what is believed tobe the best prior art alloy for the service indicated, The tool lifetests were obtained on Inconel 718 which is a commercial superalloywidely used in jet engines and considered among the mostdifficult-to-machine materials in existence. .Tool alloys of thepresentinvention were compared with the commercial high speed steelknown as M43 having the following composition:

Fe 8.7 Mo- 1.8W 3.75 Cr- 2.0V 8.2 Co 1.23C.

Each of the tools, ground to the same geometry, was used to cut the testbar of Income] 718 on a machinabliity lathe at 25 surface feet perminute, 0.0625 inch depth of cut, 0.005 inch/rev. feed, using aconventional coolant. A wear land of about 0.030 inch on the tool wasused as the end point of the test. The results of these tests are shownin Table 111.

TABLE I11 Lathe Turning Test Data On Inconel 718, BHN 375 1000F., 2 hr 2hr oil quenched The above results demonstrate that excellent tool lifehas been obtained on difficult-to-machine commercial alloys using novelalloy materials produced according to the present invention.

Alloys A 136 and A 137 are capable of being annealed so that coldpressing of their powders can be accomplished. Bar stock prepared byforging and rolling was found to be of excellent quality. Alloy A 136was found to have a coarsening temperature of 2,325 F. and an evenhigher coarsening temperature was noted for alloy A 137. The ultrafinecarbide particle size of this latter alloy was unchanged after 1 hour at2,3 50 F. Both alloys responded to quench and temper" hardeningtreatments similar to those given high sped steel. In the case of A 137,a maximum hardness of Ra 88 (Re 72) was obtained. This value is higherthan the hardness of any commercial high speed steel or cobalt base toolalloy known, and is in the range of hardness encounted in sinteredcarbides.

While there have been described and disclosed certain preferredembodiments of the invention in the foregoing specification, it will beunderstood that this invention may be otherwise embodied within thespirit and scope of the following claims.

What is claimed is:

l. A readily workable, oxide-free, thermal-resistant, alloy stockmaterial consisting essentially be weight of about 0.5 4.0 percent ofcarbon, about 60 percent of tungsten, about 0 60 percent of molybdenum,wherein the total amount of tungsten plus molybdenum is in the range ofabout 60 percent, and the balance being base metal with usual impuritiesin ordinary amounts selected form the group consisting of iron, colbalt,nickel and mixtures thereof, wherein the amount in said alloy of anyelement capable of forming an oxide having a negative free energy offormation value higher than 40 cal/gram-atom of oxygen at l,500 K. doesnot exceed the amount of such element usually present with said basemetal as an ordinary impurity.

2. An alloy according to claim 1 suitable for use as a tool alloy,wherein said alloy has a hardness above Re 56 and the ability to hold acutting edge under high temperatures generated during metal cutting andto resist softening at temperatures of l,000 F. and above.

3. An alloy according to claim 1 suitable for use as a structuralmaterial, wherein said alloy has a hardness below 'Re 56 and the abilityto withstand severe mechanical stress at elevated temperatures above 700UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO.3,698,055 Dated October 17, 1972 lnvamorfifl Frederick C. Holtz, Jr. andHugh Morrow, III

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 51; change "M 0 to "MbO Column 1, line 54, change'-CZ95K"to "-95K"1 Signed and sealed this 15th day of May 1973;

(SEAL) Attest: V

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM 0-1050 (10-69) -pc 60375-p69 .5. GOVERNMENT PRINTINGOFFICE: I959 0-365-334 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3 ,698 ,055 Dated OctQber 1972 Inventor) FrederickC. Holtz, Jr. and Hugh Morrow, III

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 51, change "M 0 to "M00 Column 1, line 54, change "-CZ95K" to -95K"L Signed and sealed this 15th day of May 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents F ORM PTO-1050 (10-69) USCOMM-DC 60376-F'59 U.S GOVERNMENTPRINTING OFFICE: 1989 0-366-334

2. An alloy according to claim 1 suitable for use as a tool alloy,wherein said alloy has a hardness above Rc 56 and the ability to hold acutting edge under high temperatures generated during metal cutting andto resist softening at temperatures of 1,000* F. and above.
 3. An alloyaccording to claim 1 suitable for use as a structural material, whereinsaid alloy has a hardness below Rc 56 and the ability to withstandsevere mechanical stress at elevated temperatures above 700* F. forprolonged periods of time.
 4. An alloy in accordance with claim 1, inwhich the alloy contains about 0 - 90 percent cobalt.
 5. An alloy inaccordance with claim 1, in which the alloy contains about 0 - 90percent nickel.
 6. An alloy in accordance with claim 1, in which thealloy contains about 0 - 90 percent iron.
 7. A fully dense, consolidatedpowder article of the alloy of claim 1.